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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

16170 results found.

  1. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  2. GRB 250327B: J-band observations with WINTER
  3. GRB 250327B: MASTER detection of OT rebrightening
  4. GRB 250327B: LCO optical counterpart detection
  5. GRB 250328A: GWAC-F50A optical upper limit
  6. FRB 20250316A: FTW optical observations
  7. GRB 250327B: CrAO and SAO RAS Optical Observations
  8. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  9. GRB 250327B: further optical observations by LCOGT
  10. EP250315a: Pan-STARRS r and i-band imaging and photometry
  11. GRB 250327b: Liverpool Telescope optical observations
  12. GRB 250322A: GRANDMA/TNOT optical upper limits
  13. GRB 250327B: Las Cumbres optical counterpart detection
  14. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  15. GRB 250327B: 1.6m Mephisto optical observations
  16. GRB 250327B: NOT spectroscopic redshift z = 3.035
  17. GRB 250327B: GOTO optical counterpart detection
  18. GRB 250327B: SVOM/VT optically bright counterpart
  19. GRB 250327B: SAO RAS optical candidate
  20. GRB 250327B: SVOM detection of a burst
  21. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  22. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  23. GRB 250327A: SVOM/VT optical candidate
  24. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  25. GRB 250327A: DDOTI Optical Observations
  26. GRB 250327A: COLIBRÍ optical upper limit
  27. EP250321a: Mondy AZT-33IK Continued Optical Observations
  28. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  29. GRB 250322A: third epoch of NOT optical observations
  30. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  31. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  32. GRB 250322A: further NOT optical observations
  33. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  34. GRB 250322A: Swift/UVOT Upper Limits
  35. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  36. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  37. EP250321a: TNOT Observation of Optical Counterpart
  38. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  39. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  40. GRB250322A: STEP/T80S optical limits
  41. GRB 250322A: Gemini-South optical observations
  42. GRB 250322A: VLT optical observations
  43. FRB 250316A: DDOTI Continued Optical Observations
  44. GRB 250322A: NOT optical upper limits
  45. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  46. GRB 250322A: MASTER optical observation
  47. EP250321a: Liverpool Telescope optical follow-up
  48. EP250321a: Mondy AZT-33IK Optical Observations
  49. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  50. EP250321a: KAIT optical observations
  51. EP250321A: COLIBRÍ Continuing Optical Observations
  52. EP250321a: WFST optical observations
  53. EP250321a: Xinglong 216 decaying optical observations
  54. EP250321a: SVOM/VT optical observation
  55. EP 250321A: Optical counterpart detection by LCO.
  56. EP250321a: Kinder optical follow-up observations
  57. GRB 250321A: Swift/UVOT Upper Limits
  58. GRB 250320B: SVOM/GRM observation of a long burst
  59. EP250321a: LCO optical counterpart detection
  60. EP250321a: Swift-XRT detection of an X-ray source
  61. EP250321A: COLIBRÍ Optical Observations
  62. EP250321a: VLT/X-shooter redshift z = 4.368
  63. EP250321a: REM optical/NIR afterglow detection
  64. EP250321a: BOOTES-5/JGT optical afterglow detection
  65. EP250321a: TRT optical counterpart detection
  66. GRB 250321A: GOTO optical upper limits
  67. EP250226a/GRB 250226A: KAIT optical observations
  68. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  69. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  70. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  71. GRB 250314A: ATCA radio upper limits
  72. EP250302a: VLA observations
  73. GRB 250317B: OHP/T193 continued follow-up
  74. GRB 250317C: SVOM/GRM observation of a long burst
  75. GRB 250317B: Leavitt Observatory optical upper limit
  76. GRB 250309B/AT2025dws: further ATCA observations
  77. GRB 250317B: Mondy AZT-33IK Optical Observations
  78. GRB 250317B: NOT optical observations suggest an optical plateau phase
  79. GRB 250317B: OHP/T193 optical observations
  80. GRB250312A: Swift/UVOT Upper Limits
  81. GRB 250317B: REM optical/NIR observations
  82. GRB 250317B: Swift-XRT observations
  83. GRB 250316A: Swift/UVOT Upper Limits
  84. GRB 250314A: REM optical/NIR upper limits
  85. GRB 250316A: AbAO AS-32 Optical Upper Limit
  86. EP 250317B: Fading optical counterpart detection by LCO
  87. GRB 250317B: LCO detection of the fading optical afterglow
  88. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  89. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  90. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  91. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  92. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  93. GRB 250314A: Swift/UVOT Upper Limits
  94. GRB 250314A: Swift XRT Detection
  95. EP250315a: optical counterpart candidate detected by Gemini North
  96. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  97. GRB 250314A: NOT near-infrared candidate counterpart
  98. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  99. EP250304a: Pan-STARRS r and i-band imaging and photometry
  100. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope

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